A disadvantage of many known sewage treatment systems is that several tanks are required for achieving not only an adequate dissolution of air or oxygen-rich gas in the waste material, but also separation of clarified liquor from a dense sludge of solid particles by allowing the sludge to form as a layer at the bottom of a separate settling tank. The overall treatment cycle of the sewage up to the stage of obtaining clarified liquor which can be safely discharged, takes a relatively long period of time in view of the fact that separate parts of the treatment cycle take place separately in different tanks.
Furthermore, a further disadvantage of such systems is that low pHs caused by high concentration of a dissolved gaseous component, such as carbon dioxide, can be detrimental to a treatment process of a liquid, typically aqueous waste material, and must be corrected by gas stripping, normally using air or an oxygen rich gas, to remove the unwanted dissolved gaseous component and/or by the addition of suitable buffering or neutralising chemicals, e.g. caustic soda.